1. Field of the Invention
The present invention is in the field of educational devices or toys and more specifically related to a manually-operated mechanical calculator for teaching the basic principles of arithmetic.
2. The Prior Art
The use of geared wheels to indicate the successive digits in a register is known at least from July 2, 1907 when U.S. Pat. No. 858,974 was issued to Glasner et al. Improvements to the basic device were presented by Fardman in U.S. Pat. No. 2,533,443 issued Dec. 12, 1950. Further variations on the basic wheeled calculator are disclosed in U.S. Pat. No. 2,797,047 issued June 25, 1957 to Lehre; in U.S. Pat. No. 3,696,995 issued Oct. 10, 1972 to Kasner; and in U.S. Pat. No. 3,706,875 issued Dec. 19, 1972, also to Kasner. The devices disclosed in the above-mentioned patents perform addition and subtraction, but include no special provision for the operations of multiplication and division. Further, none of the above patents employs removable gear wheels.
In U.S. Pat. No. 2,693,911 issued Nov. 9, 1954 to Brown, there is disclosed a manually-operated mechanical calculator having detachable registers which are used to store the results obtained in successive calculations. It will be seen that the Brown calculator is considerably different in structure and operation from the calculator of the present invention as described below.
In U.S. Pat. No. 3,436,013, issued Apr. 1, 1969 to Campbell, there is disclosed a mechanism for converting numbers from one base or modulus to another. The modulus to be used is chosen by selection of gear B, and by inserting the selected gear into the device. As described, the device is capable of performing simple addition and subtraction, but has no special provision for performing multiplication or division. The insertable gear B is not used for multiplying or dividing, but instead is used for determining the base of the number system. The mechanism disclosed by Campbell does not include provision for operating with multi-digit numbers.
In U.S. Pat. No. 3,212,200 issued Oct. 19, 1965 to Lundberg, there is disclosed an educational device in which gears of various sizes may be inserted in various arrangements. Because the device lacks a display for inputs or outputs, it might be regarded as being an analog computer rather than a digital computer. In any case, the device has no provision for carry-over and does not appear to be capable of performing the same type of arithmetic operations as the present invention.
As will be seen below, the present invention has a different structure and operates in a different manner from the calculators disclosed in the above-mentioned patents.